Filter comprising rotatable, disk-shaped filter elements

ABSTRACT

The invention concerns a device for the separation of substances, in particular of solid substances, liquid phases of varied density and/or of gases, from a liquid, by rotation with several filtering elements, which permit the filtered liquid to pass through and which are rotatably supported around a rotational axis inside of a housing, said housing exhibiting an inlet opening for the liquid, at least one discharge opening for the heavy substances separated by rotation and at least one discharge opening for the filtered liquid. In accordance with the invention, a throughflow is provided, in the region or in the proximity of the rotational axis of the filtering elements, for substances exhibiting a density lower than that of the liquid.

RELATED APPLICATIONS

The present application is the U.S. National Phase of PCT ApplicationPCT/EP02/12007, filed 28 Oct. 2002, claiming priority to German PatentApplication No. 101 54 549.5, filed 7 Nov. 2001.

BACKGROUND State of the Art

The invention concerns a device for the separation of substances, inparticular of solid substances, of liquid phases of varying densityand/or of gases, from a liquid, by rotation with several filter elementsthat allow the filtered liquid to pass through and that are rotatablymounted around an axis of rotation inside a housing that exhibits aninlet opening for the liquid, at least one discharge opening for theunfiltered components of the feed liquid separated by the rotation ofthe column of liquid and at least one discharge opening for the filteredliquid.

Such devices are exemplary in their application for wastewatertreatment. In physical processes for the treatment of effluents, thewastewater contents undergo concentration enrichment by using variousmethods depending on the physical properties of the contents such asparticle size, density and settling rate. Included amongst these are allseparating processes that use solid auxiliary materials (such as inadsorption, filtration, ion exchange), liquid auxiliary agents(extraction), gaseous auxiliary agents (flotation, stripping), thermalenergy (distillation, vaporization), gravity or centrifuging power(settling, floating). In particular, such devices find application inmembrane separation technology, that is to say, in separating processesconducted with the assistance of membranes.

Membrane separation technology devices are used in many other industrialfields of application besides wastewater treatment. By using membraneswith various pore sizes, particles ranging up to 5 nm can be separated.During the separation process, the solid substances can at least beaccumulated directly on the membrane, while the filtered liquid passesthrough the membrane. The resulting concentration polarization leads toa sedimentary deposition—also known as membrane fouling—the formation ofwhich can be influenced depending on the various types of filtrationunder operation. Classical modes of filtration operations are, on theone hand, the dead-end filtration (DEF) operation, and on the otherhand, the cross-flow filtration (CFF) operation. These essentiallydiffer from one another in that there is no forcible membrane feed flowin the case of DEF and therefore, the sedimentary deposition canaccumulate uncontrollably, while in the case of CFF, the membrane istargeted for throughflow, whereby the sedimentary deposition accumulatesin a controlled manner and can be restricted. In spite of this, aslowdown in filtrate current does occur after a longer period offiltration operation that is caused by the formation of sedimentarydeposition that is reversible. It has been common practice, both in DEFas well as in CFF operations, to conduct periodic backwashing so as toobtain a constant flow of filtrates.

The typical specific power requirement resulting from such anoperational mode as cross-flow ultrafiltration lies, for example, in therange of 3 to 7 KWH/m³ with filtrate flow rates of 100 to 150 liters/m²per hour and with a transmembrane pressure of 3 to 5 bars. For a DEFoperation, comparable values are yielded ranging from 0.1 to 0.5 KWH/m³with filtrate flow rates of 50 to 80 liters/m² per hour and with apressure of 0.5 to 2 bars. With high volumetric flow rates and a lowproduct value creation, which are indeed the case for municipal andindustrial wastewater treatment or for the exploitation of drinkingwater from surface waters, this leads to high operating costs andrenders such applications prohibitive on a widespread scale.

In the German patent DE 100 04 096, without prior publication, filteringdiscs are proposed as filtering elements that can be set into rotationaloperation, and based on their stacked manner of configuration, theyensure a very efficient filtering surface within a small space. Theformation of sedimentary deposition on the filtering discs isexclusively influenced and controlled by the centrifugal forces exertedon the suspension during operation. Over the course of testing conductedin the framework of the current invention, it became evident that in thecolumn of liquid, which is brought to rotate by the rotating filteringelements, light substances such as oils, lipids and dissolved gaseouscomponents collect in the area of the shaft, in between the filteringelements where they cause problems (clogging of the filter surface).

The objective of this invention is therefore to create a device of thetype initially depicted, in which the accumulation of light substances,between the filtering elements in the area or in the proximity of theirrotational axis, is to be avoided. To this end, the device in accordancewith the invention is to be simply constructed and cost-effectivelymanufacturable.

SUMMARY OF THE INVENTION

The objective is realized by a device for the separation of substancesfrom a liquid. Cross-flow through the filtering elements is achieved bythe application of a differential pressure. The rotational axis of thefiltering elements is basically and preferably vertically arranged inorder to best exploit the lifting effect on the light substances incountering the forces of gravity. The throughflow ensures that the lightsubstances, collecting during the operation of the device between thefiltering elements in the area or in the proximity of their rotationalaxis, can wander through the housing. In the case of substances with adensity lower than that of the liquid, we are dealing with lightsubstances such as gases, oils, lipids or gasoline, which,notwithstanding the filterable component, do not pass through thefiltering elements.

A preferred exemplary embodiment of the device is thus characterized inthat the filtering elements are basically disc-shaped, in particular,circular ring disc-shaped and the inner spaces of the filtering elementsstand in connection with the inner space of a hollow shaft through whichthe filtered liquid is led away. Thus, the filtered liquid passesthrough the filtering elements and arrives in the inner space of thehollow shaft. Preferably arranged in each filtering element, in theproximity of the hollow shaft, is at least one throughflow opening forthe unfiltered liquid. The additional throughflow openings allow thepassage of light substances through the filtering element, said lightsubstances being found in the liquid that, due to their low specificgravity, collect in the area of the rotational axis of the filteringelements. Because the filtering elements rotate around their rotationalaxis during operation, the light substances floating upward in thehousing can rise up through all of the filtering elements, and can do soeven in those instances where there is only one single throughflowopening in each filtering element.

Another preferred exemplary embodiment of the device is thuscharacterized in that the throughflow openings in the filtering elementsare essentially arranged at an equal radial distance from the hollowshaft in alignment. In particular, when the filtering elements arestanding still or are rotating slowly, this ensures a direct throughflowthrough several filtering elements that are axially spaced apart fromone another in their arrangement on the hollow shaft.

Another preferred exemplary embodiment of the device is thuscharacterized in that the filtering elements are basically designed tobe circular ring disc-shaped and the inner spaces of the filteringelements stand in connection with the inner space of a hollow shaft,arranged concentrically to the rotational axis of the filteringelements, via several hollow spokes, spaced apart from one another inthe circumferential direction, through which said hollow shaft thefiltered liquid is led off. The hollow spokes have a double function. Onthe one hand, they provide a fluid passage connection between thefiltering elements and the hollow shaft. On the other hand, they permitthe passage of light substances in the proximity of the hollow shaft inthe direction of the rotational axis of the filtering elements.

Another preferred exemplary embodiment of the device is thuscharacterized in that an additional discharge opening is arranged in theupper face of the housing, in the proximity of the hollow shaft. Theadditional discharge opening serves the purpose of letting out lightsubstances that have risen to the upper face of the housing by passingthrough the throughflow openings in the filtering elements or in betweenand through the spokes, based on their being driven upward. The heavysubstances, separated by the rotation of the column of liquid in thedirection of the housing wall, whose density is greater than that of themainstream liquid, can be drawn off through a discharge opening in thehousing wall in the proximity of the housing base.

Another preferred exemplary embodiment is thus characterized in that thefiltering elements are essentially designed as circular ring disc-shapedand stand in connection with a ring chamber that is concentricallyarranged in relation to the rotational axis of the filtering elements,radially outside of the filtering elements. The ring chamber serves toreceive the filtered liquid. The arrangement of the receiving space forthe filtered liquid, being radially outside of the filtering elements,provides the advantage that the centrifugal forces at work duringoperation serve to promote the flow of the current into the receivingspace. Furthermore, a central throughflow passage is formed radiallyinside of the filtering elements, said passage ensuring the unhinderedupward rising action of the light substances.

Another preferred exemplary embodiment of the device is thuscharacterized in that filtering elements are connected to a drum in atorsionally secure manner, said drum being rotatably supported in thehousing and allowing the filtered liquid to flow through in the area ofthe filtering elements. The filtering elements can be brought to rotatetogether via the drum. The throughflow design of the drum in the area ofthe filtering elements ensures that the filtered liquid can exit out ofthe filtering elements.

Another preferred exemplary embodiment of the device is thuscharacterized in that the drum is essentially designed in a circularcylinder shape, and that, on the lower front face of the drum, an inletport is provided for the liquid, and that, on the upper front face ofthe drum, an outlet port is provided for light substances. By thisarrangement, it is ensured that the light substances will arriveunobstructed at the outlet port based on their upward driven lift.

Another preferred exemplary embodiment of the device is thuscharacterized in that the inlet port and the outlet port areconcentrically arranged in relation to the filtering elements and areused to support the drum. The resulting simple design of the deviceresults in low series production costs. Furthermore, it isadvantageousthat the drum can be preassembled together with thefiltering elements.

Another preferred exemplary embodiment of the device is thuscharacterized in that, in the lower portion of the housing, a dischargeopening is provided radially on the outside, which stands in connectionwith the interior of the drum. Based on its radially externalpositioning, the discharge opening serves to permit the discharge ofsolid substances, filtered out of the liquid, that exhibit a specificdensity that is greater than that of the liquid.

Further advantages, characteristics and specifics of the inventionemerge from the following description, which elaborates on the variousdesign embodiments in detail while referring to the drawings. Shown in:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first design embodiment of the device in accordance withthe invention, seen in longitudinal cross section;

FIG. 2 shows an individual filtering element from the device illustratedin FIG. 1, seen in top view;

FIG. 3 shows an individual filtering element from the device illustratedin FIG. 1, in accordance with a second design embodiment of theinvention, seen in top view;

FIG. 4 shows a third design embodiment of the device in accordance withthe invention, in longitudinal cross section and

FIG. 5 shows an individual filtering element from the device illustratedin FIG. 4, seen in top view.

DETAILED DESCRIPTION

The device illustrated in FIG. 1 comprises a housing 1, in which ahollow shaft 2 is rotatably taken up around a rotational axis 3.Connected to the hollow shaft 2 are numerous torsionally securefiltering elements 5, 6, and 7, which are all designed in the samemanner. In the design embodiment illustrated in FIG. 1, there are 19filtering elements connected to the hollow shaft 2 in a torsionallysecure manner. The hollow shaft 2 can be designed of one piece orcomprised of several parts. The filtering elements are comprised ofmembranes and are hollow on the interior. Through the membranes, liquidcan penetrate from the outside into the interior of the filteringelements from where it then arrives at the interior of the hollow shaftby way of suitable openings in the shell surface of the hollow shaft.The filtering elements 5, 6 and 7, are secured by cylindrical shells 10,11 and 14, in the axial direction. The cylindrical shells 10, 11 and 14can be equipped with gaskets to seal off the interfacing sites betweenthe filtering elements and the hollow shaft.

The direction of rotation of the hollow shaft 2 with the filteringelements 5, 6 and 7 is indicated by an arrow 16. The lower end 18 of thehollow shaft 2 is designed to be closed and is rotationally supported ina lower cover 20, which seals off the housing 1 on the bottom. By meansof screw connections 22 and 23, the lower cover 20 is secured to aflange 25, which, on the outside, is radially secured to the lower edgeof the housing 1. In the lower cover 20, there is also an inlet opening28 provided for a liquid yet to be filtered that is indicated by anarrow 30. In proximity there, a discharge opening 56 is also provided,in the direct vicinity of the housing wall, through which heavysubstances, with densities greater than that of the liquid, can be drawnoff after separation by rotation and accumulated concentration upagainst the wall.

The upper end 32 of the hollow shaft 2 is supported in an upper cover34, which seals the housing 1 off on the top. The upper end 32 forms adischarge opening for the filtered liquid, or the so-called filtrate.The released filtrate is indicated by an arrow 36.

The entering liquid 30 arrives into the interior of the housing 1 by wayof the inlet opening 28 and from there, it emerges into the hollow shaft2 by way of the filtering elements 5, 6 and 7 as a filtrate and exitssaid hollow shaft through the upper end 32 of the hollow shaft 2.

By means of screw connections 38 and 39, the upper cover 34 is securedto a flange 41 that, on the outside, is radially mounted to the upperedge of the housing 1. In the proximity of the shell surface of thecircular cylinder shaped housing 1, a discharge opening 44 is designedin the upper cover 34 for the concentrates yielded by the enteringliquid 30. Radially further inward, away from the discharge opening 44,a discharge opening 46 for light substances is designed in the uppercover 34, in the proximity of the hollow shaft 2.

As a result of the rotational movement of the hollow shaft 2 executedduring operation and of the torsionally secure filtering elementsconnected to said shaft, the column of liquid located in the housing 1is set into circular motion. The centrifugal forces resulting from thisensure that the substances contained in the liquid will wander into thefield of the centrifugal forces. Heavier active substances will betransported away in the countercurrent to the lighter substances. Suchsubstances are designated as heavier substances that exhibit a specificdensity greater than that of the liquid. Other substances are designatedas lighter substances that exhibit a specific density lower than that ofthe liquid. The heavier substances contained in the entering liquid 30are radially propelled outwards under the operation of the separatingdevice due to their density and they collect in the region of the shellsurface of the housing 1, where they can exit through the dischargeopenings 44, 56 out of the housing 1. The light substances collect onthe outer shell surface of the hollow shaft 2 due to their low density.The movement of the heavier substances is effected by a current on theinterior of the device, acting from below and rising upward.

According to the current invention, throughflow openings 48 are designedin the circular ring disc-shaped or circular disc-shaped filteringelements 5, 6 and 7. As can be seen in FIG. 1, the throughflow openings48 are respectively arranged radially equidistant to the rotational axis3 of the hollow shaft 2. As a result of the rotational movement of thehollow shaft 2 in unison with the filtering elements 5, 6 and 7, it isensured during the operation of the separating device that lightsubstances, which collect in the region of the hollow shaft 2 due totheir low density, will rise upward to the discharge opening 46, andwill be able to wander or flow out.

As can be seen in FIG. 2, the individual filtering elements 5 of theseparating device illustrated in FIG. 1 are designed as a circular ringdisc provided with a central opening 49. The central opening 49 of theinternally hollow filtering elements ensures that the filtrate canarrive from the interior of the filtering elements into the hollow shaft2 via the corresponding openings. The centrifugal forces effect thecontinuous deportation of the sedimentary deposition (concentrationpolarization) from the filter surface of the circular disc or circularshaped filtering elements and ensure a continuous and smooth flowthrough the membrane. The ratio of the filtrate volume to the feedvolume determines the concentration of the non-filterable substances inthe yield 44, 56.

In FIG. 3, an alternate embodiment form of the filtering element 50 isrepresented. The filtering element 50 is also designed as a circularring disc, however, it is provided with a larger central opening 51 thanthe filtering element 5 represented in FIG. 2. From the central opening51, hollow spokes 52, 53, 54 and 55 extend outward, which radially runinward and connect the interior of the filtering element 50 to thehollow shaft 2. It is self-evident that in the region of the interfacingsites between the spokes 52 through 55 and the hollow shaft 2,corresponding openings are provided in the hollow shaft 2 which allowthe filtrate to pass through. At the same time, the spokes 52 through55, in a state of integration with the filtering element 50, ensure thatthe light substances can penetrate unobstructed through the spokes 52 to55, in the direction of the rotational axis 3 of the hollow shaft 2.This guarantees the nearly unhindered upward rise of light substances inthe region of the hollow shaft 2.

In FIG. 4, another design embodiment of a separating device inaccordance with the invention is represented. The separating device iscomprised of a housing 60, in which a circular cylinder-shaped drum 61is rotatably mounted. On the lower front face of the drum 61, a hollowopen-ended tap 62 is arranged that enables the entry of the liquid to befiltered into the interior of the drum 61. On the upper front face ofthe drum 61, a hollow open-ended tap 63 is arranged that enables theexit of light substances out of the interior of the drum 61.

The housing 60 is sealed off on the bottom by a base 65 and on the topby a cover 64. The housing 60 is designed in the shape of a circularcylinder, just as the drum 61, and exhibits a somewhat larger diameterthan the drum 61. The drum 61 is supported by the hollow taps 62 and 63in the base 65 of the housing 60 and in the cover 64 of the housing 60.

There is a plurality of filtering elements 66, 67 that are outwardlyradially connected with the shell surface of the drum 61 in atorsionally secure manner. The filtering elements 66, 67 are secured inthe direction of the rotational axis 3 by means of ring fasteners 68,69, 70. Furthermore, the ring fasteners 68, 69, 70 also serve to sealoff the interfacing sites between the filtering elements 66, 67 and theshell surface of the drum 61. In the region of the filtering elements,the drum allows the filtered liquid to pass through. The filteringelements 66, 67 have the shape of circular ring discs with a centralthroughflow opening 72, as can specifically be seen in FIG. 5. Thecentral throughflow openings 72 ensure that light substances, whichcollect in the region of the rotational axis 3 of the drum 61 during theoperation of the separating device, are able to rise unobstructed to thedischarge opening 63. A discharge opening for heavy substances isradially provided outside on the upper edge of the drum 61 and isdesignated by 73. Heavy substances arrive into the hollow formed cover64 via the discharge opening 73 and from there, into a discharge opening74 that is radially provided on the outside of the cover 64. Anadditional discharge opening for heavy substances is provided radiallyon the outside, on the lower edge of the drum 61 and is designated by80. Heavy substances arrive into the hollow formed base 65 via thedischarge opening 80 and from there, into a discharge opening 79 that isradially provided on the outside of the base 65. An additional dischargeopening 71 may be provided on the outer surface of the housing 60.

The filtering elements 66, 67 are provided with outward radialthroughflow openings 78 running in the direction of the rotational axis3 of the drum 61. The throughflow openings 78 ensure the passage ofsolid substances and thus prevent sedimentary clogging of the filteringelements on the radial exterior. In the lower front wall of the drum 61,one or several throughflow openings are radially provided on the outside(not represented here). They allow the passage of solid substances,exhibiting a specific weight that is greater than that of the liquid tobe filtered, to pass through at least one discharge opening 79, which isradially arranged on the outside in the lower front wall of the housing60. The circular ring shaped filtering elements can also be designed assegments in such a manner that gaps allow the passage of solid bodies,or they can be arranged as in turbines.

During the operation of the filtering device represented in FIGS. 1through 5, a liquid to be filtered, such as a suspension, for example,is fed via a pump through the inlet opening 28, 62 into the housing 1,and into the drum 61. The liquid is drawn in through the filteringelements and is drawn out through the hollow shaft standing in flowassociation with the filtering elements or via the ring chamber betweenthe drum 61 and the housing 60. Based on the movement of the liquidoccurring during the rotation of the filtering elements and on thecentrifugal forces effected on the liquid, it is possible to effectivelyprevent an undesirable buildup of sedimentation on the filteringelements. The transmembrane pressure required for filtration can beimplemented, for example, by the application of a negative pressure onthe filtrate side or by the application of a positive pressure on theinlet opening of the separating device. Furthermore, it is beneficial touse the hydrostatic or hydrodynamic pressure present in many of thewater treatment systems for the purpose of generating the requiredtransmembrane pressure and suitable for the application of the describedseparating device. Modern water treatment plants exhibit, for example,aeration reactors as tall as 20 meters in which a transmembrane gradientpressure of nearly 2 bars can be generated by hydrostatic pressure.

The filtering elements can be designed as hollow bodies or as hollowframes exhibiting membranes or covered over by membranes. To this end,conventional industrial membrane applications from ultrafiltrationmembrane technology can be used such as for example, polymer membranes,membrane filters, ultrafiltration membranes, microfiltration membranesor nanofiltration membranes.

The hollow shaft 2 represented in FIG. 1 can be constructed of one pieceor from several parts comprised of various hollow sections, for examplein the shape of a cylinder, whereby the various sections of the hollowshaft are separated by filtering elements interposed between saidsections, in particular by filtering discs, and said sections beinginterconnected by the latter discs are impermeable to the liquid yet tobe filtered. It remains essential that, between the interior of thehollow shaft, or between the interior of the ring chamber, between thedrum and the housing, a fluid continuum be established in the form of atleast one opening that makes it possible for the filtrate to passthrough.

The separating or the filtering device can be used in aerobic as well asanaerobic operating systems, for example for the treatment of wastewater or for water purification systems. The filtering device can, forexample, be integrated in the activated sludge stage of a sewagetreatment plant and represents a modern system for biomass hold-up andtherefore, for the enrichment of the biomass. It is self-evident thatthe filtering device can also be applied in the resolution of the sewagefeed headed for the sewage treatment plant after or in place ofpreliminary clarification. This permits the separation of the feed intoa carbon-rich concentrate, which can be anaerobically converted tobiogas and into a carbon-poor filtrate, which can be aerobicallyconverted in high performance wastewater reactors for example. Ofcourse, it is also possible to use the filtering device to obtaindrinking water from surface waters. The separating device can also beindicated for use in installations in which air or gas is introduced,thus making an aerobic mode of operation possible.

Preferably, the housing 1, 60 essentially has the shape of a circularcylinder whose longitudinal axis, preferably in the vertical direction,is arranged perpendicular to a horizontal foundation. The rotationalaxis of the filtering elements is also preferably oriented in a verticaldirection as well, thus perpendicular to a horizontal foundation.Furthermore, the inlet opening 28, 62 into the housing 1 and into thedrum 61 is arranged in the base of the housing 1 or in the lower cover20 or in the lower front face of the drum 61. This configuration ensuresthat light substances contained in the housing 1 or in the drum 61 willrise parallel or alongside the rotational axis 3 of the filteringelements. In accordance with the invention, the nearly unobstructedascent of light substances is made possible by the throughflow openings48, the spokes 52 through 55 and/or by the central throughflow openings72.

1. A device for the separation of substances from a liquid comprising: ahousing having a first end and a second end opposite the first end; ahollow shaft extending generally between the first end and the secondend of the housing and generally along the center of the housing, thehollow shaft being rotatable about a rotational axis extending throughthe center of the hollow shaft; a plurality of generally disc shapedfiltering elements disposed in the housing and attached to the hollowshaft so as to be rotatable in conjunction with the shaft, the filteringelements comprising an outer surface and an inner space, the innerspaces being fluidly connected to the hollow shaft so as to allow afiltered liquid to pass through the outer surfaces and through the innerspace and into the hollow shaft; wherein at least one throughflowopening is provided in the filtering elements in the proximity of thehollow shaft configured for allowing substances with a density lowerthan that of the liquid to flow past the filtering elements; and whereinthe hollow shaft defines a discharge opening for the filtered liquid;wherein the housing comprises an inlet configured for ingress of theliquid, a first outlet configured for egress of heavy substances, and asecond outlet configured for egress of light substances, and wherein thefirst outlet and the second outlet are both disposed on the first end ofthe housing; and wherein the first outlet is disposed near the outerdiameter of the first end of the housing and wherein the second outletis disposed near the hollow shaft.
 2. The device in accordance withclaim 1, wherein the inlet is disposed on the second end of the housing.3. The device in accordance with claim 2, wherein the at least onethroughflow opening comprises a plurality of throughflow openings, andwherein the throughflow openings in the filtering elements areessentially arranged to be radially equidistant to the hollow shaft. 4.The device in accordance with claim 1, wherein the filtering elementsare ring-shaped discs.
 5. A device for the separation of substances froma liquid comprising: a device configured for separating a liquid into afirst filtered liquid, a second liquid having a density, and a thirdliquid having a density which is greater than the density than thesecond liquid; the device comprising: a housing having a first end and asecond end; a plurality of generally disc shaped filtering elementsdisposed within the housing so as to be rotatable within the housing,the filtering elements having outer surfaces and inner spaces and beingconfigured for allowing filtered liquid to pass through the outersurfaces and into the inner spaces; a hollow shaft disposed between thefirst end and the second end of the housing and having the plurality offiltering elements attached thereto, the hollow shaft having an innerspace disposed in communication with the inner spaces of the filteringelements such that the first filtered liquid passes from the innerspaces of the filtering elements to the inner space of the hollow shaft,the hollow shaft being rotatable within the housing in conjunction withthe filtering elements; wherein the filtering elements have at least onethroughflow opening proximate to the hollow shaft configured forallowing substances with a density lower than that of the third liquidto flow past the filtering elements; and wherein the hollow shaftdefines an outlet for the first filtered liquid, and wherein the housingcomprises an inlet for the liquid which is to be separated disposed onthe first end of the housing, a first discharge outlet for dischargingthe second fluid disposed on the second end of the housing, and a seconddischarge outlet for discharging the third fluid disposed on the secondend of the housing; and wherein the first discharge outlet is disposedadjacent the hollow shaft and the second discharge outlet is disposedadjacent the outside diameter of the housing.
 6. A device for theseparation of substances from a liquid, the device comprising: aplurality of filtering elements configured for rotating around anessentially vertically arranged rotational axis, said filtering elementsbeing configured to allow filtered liquid to pass through and which arerotatably supported around the rotational axis in a housing, saidhousing having a first end and a second end opposite the first end, thehousing having a lower inlet opening for the ingress of said liquiddisposed on the first end of the housing, a first discharge openingdisposed on the second end of the housing adjacent the outside diameterof the housing and configured for discharging the heavy substancesseparated by rotation, a second discharge opening disposed on the secondend of the housing adjacent a central axis of the housing, said axisextending between the first and second end of the housing, andconfigured for discharging the light substances separated by rotation,and a filter discharge opening for filtered liquid, wherein thefiltering elements, in the region or in the proximity of the rotationalaxis of the filtering elements, have at least one throughflow openingthrough which substances exhibiting a density lower than that of theliquid rise upward, counter to the gravitational force.
 7. The device inaccordance with claim 6, wherein the filtering elements are essentiallydesigned as circular ring disc shaped and stand in connection with aring chamber, said ring chamber being arranged concentrically relativeto the rotational axis of the filtering elements, radially outside ofthe filtering elements.
 8. The device in accordance with claim 6,wherein the filtering elements are torsionally securely connected with adrum, said drum being rotatably mounted in the housing and allowing, inthe area of the filtering elements passage of the filtered liquid. 9.The device in accordance with claim 8, wherein the drum is essentiallycylinder shaped having a lower end and an upper end, and wherein aninlet port for the fluid is provided on the lower end as an inletopening and an outlet port is provided on the upper end as a dischargeopening for the light substances.
 10. The device in accordance withclaim 9, wherein the inlet port and the outlet port are arrangedconcentrically relative to the filtering elements and are used forsupporting the drum.
 11. The device in accordance with 8, wherein, inthe lower region of the housing, a third discharge opening is providedradially on the outer side, said discharge opening standing inconnection with the interior of the drum.
 12. A process for theseparation of substances from a liquid, by means of a device withseveral rotatable filtering elements arranged around a rotational axisand in stacked formation, said filtering elements allowing the filteredliquid to pass through, the process comprising introducing liquid intothe device through a fluid inlet disposed on a first end of the device,collecting between the filtering elements in the area of the rotationalaxis lower density substances which do not pass through the filteringelements and which exhibit a density lower than that of the fluid,allowing said lower density substances to pass by the filtering elementsvia at least one throughflow opening provided in the filtering elements,discharging said lower density substances through a first dischargeoutlet disposed on a second end of the device opposite the first end ofthe device, said first discharge outlet being disposed adjacent therotational axis of the filtering elements, collecting a higher densitysubstance proximate the outer diameter of the filtering elements,discharging said higher density substance through a second dischargeoutlet disposed on the second end of the device, said second dischargeoutlet being disposed adjacent the outer diameter of the filteringelements, and collecting the filtered liquid which passes through thefiltering elements and discharging said filtered liquid through a thirddischarge outlet.